Micro-components, such as, but not limited to, microelectronic, micro-optoelectronic, and microelectromechanical systems (MEMS), share a common fabrication technology wherein a plurality of interconnected microcircuits are made within and upon a substrate. This substrate is commonly referred to as a die or microelectronic die. A microelectronic package, for example, comprises a microelectronic die electrically interconnected with a carrier substrate, and one or more other components, such as electrical interconnects, an integrated heat spreader, a heat sink, among others. An example of a microelectronic package is an integrated circuit microprocessor, wherein the microelectronic die comprises integrated circuits.
A die commonly comprises an active side having electrical interconnects and a die backside that provides a broad surface suitable for coupling with a heat dissipation device, also referred to as a thermal management system. A die generates heat as a result of the electrical activity of the internal microcircuits. In order to minimize the damaging effects of this heat, passive and/or active thermal management systems are used to dissipate the heat. Such thermal management systems include heat sinks, heat spreaders, and fans, among many others and combinations, that are adapted to thermally couple with the die backside. There are limitations in the use of each type of thermal management system, and in many cases, the thermal management system is designed specifically for a particular die, package design and/or intended operation, limiting cross-platform compatibility.
Integrated heat spreaders (IHS) are passive thermal conducting lids or caps placed in thermal engagement with the die backside. Integrated heat spreaders comprise a housing having a broad flat top and perimeter sides defining a cavity. The IHS is placed over the die with the die contained within the cavity, with the inside surface of the top in thermal engagement with the die backside. The free edges of the perimeter sides provide an interface for which to bond the IHS to the carrier substrate. The IHS provides a sealed housing protecting the die, as well as an enlarged planar top surface for thermally coupling with another component of a thermal management system, such as a heat sink.
A heat sink provides a large thermal mass with a large surface area relative to the backside of the die. The heat sink is coupled in thermal engagement with the die backside, commonly by way of an IHS as an interface, for conducting heat from the die to the heat sink. The heat sink provides an enlarged surface area, primarily by way of a plurality of appendages, commonly fins or pins, to convectively transfer heat to the surrounding environment. Heat sinks tend to be very large and have sophisticated design with regards to the appendages. In some cases, a fan is coupled to the heat sink to further enhance convective heat transfer to the environment.
A heat sink is commonly coupled to an IHS with a thermal interface material (TIM), such as a grease having a relatively high thermal conductivity, between the opposing surfaces of the heat sink and IHS. The TIM accommodates for any surface irregularities to ensure that the opposing surfaces are in full thermal engagement. The TIM, therefore, reduces the thermal resistance at the interface between the IHS and the heat sink. The heat sink is commonly secured to the IHS with a hold-down clip or other retention mechanism.
Non-uniform power distribution across the die results in localized high heat flux areas, referred to as hot spots, on the die backside. The thermal management system must be able to maintain these high heat flux areas at or below a specified temperature. This is very difficult when the heat flux of the high heat flux areas can be 10-times the average across the die backside. Current thermal management systems are limited in their ability to mitigate these high heat flux areas.
The IHS does not have a major effect on distributing the heat evenly across the die backside. An uneven heat distribution across the die backside causes a number of issues. For example, the thermal management system must be sized to manage the highest expected temperature associated with the high heat flux areas. Further, the temperature difference across the die can cause mechanical stresses at the electrical interconnects due to uneven thermal expansion. Also, the internal microcircuits operate more efficiently when at a uniform operating temperature.
One major factor contributing to the limitations of current thermal management systems is the relatively high thermal resistance between the IHS and the heat sink. The thermal resistance at the interface with the available TIM is not low enough to adequately provide the necessary thermal mitigation in a reasonably sized system. Issues of excessive thermal management system size, weight, complexity, and cost become driving factors in new microelectronic package design.
Active cooling technology utilizing fluid to assist in the transport of heat away from the die has been attempted and shows great promise. Such systems currently require complex fabrication techniques that are difficult to incorporate into the existing microelectronic package fabrication and assembly line, as well as being cost prohibitive.